It's official: Letting a baby cry itself to sleep is neither cruel nor bad for the mental health of the child or its parents.

According to researchers at the Royal Children's Hospital in Melbourne, what they call the controlled crying technique helps resolve sleeping problems and wards off depression in mothers.

Rather than immediately tending to a crying child, parents steeled themselves and waited for it to settle back to sleep.

Babies under 6 months were not left alone because they needed to be fed during the night.

The Melbourne researchers tried the technique with 328 infants aged 8-10 months old and found that in 45 percent of cases sleeping problems were reduced.

In a follow-up study of 23 of the children aged 6, they found no adverse behavior or increased incidence of depression among mothers.

"Hopefully, this evidence really will reassure parents who want to manage their children's sleep by using these kind of strategies," researcher Anna Price says.

"We totally understand that hearing your baby crying is difficult for any parent, but it's great to know if they persevere they aren't doing their child any harm."

The findings come at the end of a six-year study and were presented at the World Health Congress of Internal Medicine in Melbourne this month.

The gathering was told that controlled crying cut babies' sleeping problems by 30 percent within four months and cut depression in mothers by 40 per cent by the time their child reached 2.

While 85 percent of parents said controlled crying had helped them bond with their baby, the remaining 15 percent reported that there had been no change. None said the technique caused harm.